This review addressed a well-defined question for participants, interventions, outcomes, and study design. Relevant databases were searched, but the restriction to English language and the lack of apparent attempts to retrieve unpublished studies, means that the potential for language and publication bias could not be ruled out. Screening of the studies and data extraction was undertaken in duplicate.
The authors did not report that they assessed quality of these studies, which means the reliability of the findings was uncertain. The characteristics of the individual trials were presented. Potential sources of heterogeneity were explored. As heterogeneity was found in the studies, it may not have been appropriate to pool the data. Also, multiple publication of the same study may have been included in the meta-analysis, leading to potential double-counting. The authors acknowledged the limitations of the review.
The potential for missed data, together with weaknesses and clinical heterogeneity in the included studies, mean that the authors' conclusions should be interpreted with some caution.